We shall extend our current investigations of reaction sequences used for aromatic acid catabolism by a yeast isolated from soil, Trichosporon cutaneum. This organism grows at the expense of a wide range of phenolics and aromatic acids, and yet it lacks some of the dioxygenases commonly encountered in bacteria, such as those for protocatechuic, homoprotocatechuic and gentisic acids; nevertheless, these compounds are completely metabolized after growth with benzoate and other substrates. Our working hypothesis, for which we now seek additional support, is that these compounds and others can be degraded after a third hydroxyl group has been introduced into the nucleus, so that ring-fission can then occur. This metabolic strategy, in turn, depends upon the use of various enzymes that have broader substrate specificities than their counterparts in procaryotes: those currently under investigation include salicclate and 3-hydroxyphenylacetate hydroxylases, and homogentisate dioxygenase. Patterns of enzyme derepression in T.cutaneum lack sharp definition and cannot be used for delineating metabolic routes; but with the successful application of other approaches, it is now possible to identify derepressors of enzymatic sequences as they become known. Our investigations of the bacterial catabolism of naturally-occurring aromatic acids bearing three methoxyl group substituents will be assisted by the use of synthetic substrates labeled in these groups with 14C and 13C. By these procedures, groups that give rise either to CO2 or to methanol can be identified unequivocally.